Centrifugal rotor

ABSTRACT

A centrifugal rotor includes a hub ( 10 ) having a longitudinal axis ( 8 ), a fluid inlet ( 20 ), a first flange referred to as upstream flange ( 12 ) and having an opening ( 22 ) around the hub ( 10 ), a second flange referred to as downstream flange ( 14 ) separated from the first flange by blades ( 16 ) thus forming ducts each delimited by the first flange ( 12 ), the second flange ( 14 ) and two blades ( 16 ) and extending from the fluid inlet ( 20 ) to a peripheral outlet ( 26 ), near the peripheral outlet ( 26 ) the first flange ( 12 ) having a concave zone ( 32 ) facing towards the ducts whereas the second flange ( 14 ) has a convex zone ( 34 ) facing towards the ducts.

BACKGROUND OF THE INVENTION

The present invention relates to a centrifugal rotor.

The technical field of this invention is that of the fluid, liquid orgaseous compression. The invention therefore relates to both pumps aswell as compressors which make a supply of liquid or gas respectivelypossible, from a given pressure to a higher pressure.

There are many techniques to increase the pressure of a fluid. A commontechnique consists in centrifuging the fluid upon which stress isexerted which in turn causes an increase in its pressure. For theimplementation of this technique, there are many different structures ofpumps and compressors depending upon many parameters including therelated fluid, the environment (size, etc.) and desired performance(compression rate, etc.). Subsequently, we will focus on pumps andcompressors comprising at least one centrifugal rotor associated with anaxial diffuser.

A centrifugal rotor is a rotor having an axis of rotation. It isdesigned to compress a fluid flowing in a direction parallel to its axisof rotation, the compressed fluid leaving the rotor in a radialdirection outwardly. When the compressed fluid must flow axially, onesolution is to direct the fluid exiting the rotor so that it changes thedirection of flow. The element used for this purpose is a fixed partcalled an axial diffuser and it has at least one duct to direct thecompressed fluid. The downstream end of the duct, that is to say the endwhich is remote from the centrifugal rotor, is axially oriented inaccordance with the direction that one wishes to direct the compressedfluid. The purpose of the axial diffuser is to then take a turn at about90° to the outgoing fluid from the centrifugal rotor so as to guide itaxially.

Document FR-2874241 discloses a high-efficiency centrifugal rotor whichuses truncated blades with a radial diffuser. The wake of the bladerecloses in the diffuser and by working with the wakes of the otheradjacent blades creates a stratified flow that gradually expands withinthe diffuser. We thus find in this document a rotor incorporating adiffuser. The very thick blades are located in the lower part of therotor.

U.S. Pat. No. 1,447,916 illustrates another embodiment of a rotorincorporating a diffuser. The latter may be a single piece with therotor portion comprising blades or it may be a separate piece secured tothe rotor portion comprising the blades. Although it is noted that inall the figures illustrating the vanes, they only extend over one partof the device (corresponding to the centrifugal rotor) and not to theperipheral output of the device and that the portion corresponding tothe centrifugal rotor has a perfectly radial outlet upstream from thediffuser.

One technical problem encountered with such a structure is that it isthe source of pressure loss in the compressed fluid. It is indeed knownthat when a fluid flows, it undergoes pressure losses that depend on theconduit in which it is found, including any changes in directionundergone.

OBJECTS AND SUMMARY OF THE INVENTION

It is not possible to eliminate the pressure drop that are particularlyrelated to the nature of the fluid itself (particularly its viscosity)but this invention is to provide the means to minimize as much aspossible these losses.

An object of this invention is thus, for a given compression stage,comprising a centrifugal rotor and an axial diffuser, to increase theperformance of this stage, i.e., for example, obtaining a highercompression ratio for a given power or for a given compression reducingthe mechanical power needed to be exerted on the rotor to make it turn.

To this end, this invention proposes a centrifugal rotor including:

a hub having a longitudinal axis,

a fluid inlet,

a first flange, upstream and having an opening around the hub,

a second flange, separated downstream from said first flange by thevanes thereby forming channels each delimited by the first flange, thesecond flange and two vanes extending from the fluid inlet to aperipheral outlet.

According to this invention, in the proximity of the peripheral outlet,the first flange has a concave area oriented towards the channels whilethe second flange has a convex area oriented towards the channels.

Due to the form thus given to the outlet channels, the passage of aradial flow within the centrifugal rotor to an axial flow in thediffuser upstream from the rotor is performed less brusquely making itpossible to limit the losses in pressure when the fluid changesdirection.

To have a rotor that is simple to produce, the first flange and thesecond flange advantageously have a circular shape around thelongitudinal axis.

For example it is anticipated that the surface tangent to the concaveregion of the first flange exiting the channel, forms an angle ofbetween 1° and 45°, preferably between 10° and 30°, with a radial planeperpendicular to the longitudinal axis. Likewise, it is anticipated thatthe surface tangent to the convex region of the second flange exitingthe channel, forms an angle of between 1° and 45°, preferably between10° and 30°, with a radial plane perpendicular to the longitudinal axis.

To better guide the fluid in a centrifugal rotor according to theinvention, it is advantageously provided that the vanes extend to theouter peripheral exterior edge of the first flange and/or of the secondflange.

To easily create an acceleration of the fluid exiting the centrifugalrotor, the first flange advantageously has an outer peripheral edgeadjacent to the channels which have a greater diameter than an outerperipheral edge adjacent to the channels of the second flange. At theedge with the greater diameter, which corresponds to the outside of thecurved shape given to the outlet of the centrifugal rotor, the speed istherefore higher. This is preferable because the path to be traveledalong the outside of a turn is greater than that of the inside of aturn. In this way, a more uniform distribution of the velocity ispromoted when the fluid then moves in a substantially longitudinaldirection.

This invention further relates to a centrifugal compressor and/or acentrifugal pump comprising a centrifugal rotor as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

Details and advantages of this invention will become more apparent fromthe following description with reference to the accompanying drawings inwhich:

FIG. 1 illustrates a centrifugal rotor of the prior art with a crosssectional view of a half rotor mounted in a compressor,

FIG. 2 is a view similar to that of FIG. 1 for a centrifugal rotoraccording to a first embodiment of this invention,

FIG. 3 is a view similar to the preceding views according to a secondembodiment of this invention, and

FIG. 4 is a cross-section view in perspective along the cut line IV-IVof FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

Those skilled in the art will recognize a centrifugal rotor 2 in FIG. 1mounted inside a housing 4, for example a compressor housing, and ashaft 6 having a longitudinal axis 8. The following description will bemade with reference to a working air compressor (or more generally agaseous fluid compressor), but this invention may also be applied topumps for liquids.

When the centrifugal rotor 2 is rotated by the shaft 6, the air (orother gaseous fluid) is drawn into the centrifugal rotor 2 in alongitudinal direction relative to the longitudinal axis 8, and isdriven in a mixed flow motion in the centrifugal rotor 2 while rotatingand appear radially with respect to the longitudinal axis 8.

The centrifugal rotor 2 is built in one piece and comprises a hub 10, afirst flange or upstream flange 12, a second flange or downstream flange14 and vanes 16.

The hub 10 enables a connection between the shaft 6 and the centrifugalrotor 2. It has an overall circular, cylindrical, tubular shape and isprovided with a means to fasten it to the shaft 6. For example, alongitudinal groove is typically provided in the hub 10 and the shaft 6to receive a longitudinal spline or even grooves, or any other type ofconnection.

The downstream flange 14 is connected directly to the hub 10 and extendsradially relative to the longitudinal axis 8. The upstream/downstreamdirection is defined relative to the direction of the air flow in thecentrifugal rotor 2. Indeed, in FIG. 1 (as well as in the other figures)air is drawn to the right of the rotor and then moves longitudinally tothe left before being driven in a radial direction to be orientedfinally, after leaving the centrifugal rotor 2 in a longitudinaldirection back towards the left of the figure. Thus the upstreamelements are arranged to the right of the downstream elements in thefigures.

The upstream flange 12 faces the downstream flange 14 and is connectedthereto by the vanes 16 thereby defining the channels for the airbetween the two flanges. The air is thus introduced between the innersurfaces of the flanges and vanes in a centrifugal radial manner.

The upstream flange 12 does not extend to the hub 10 but remains at adistance therefrom. A sealing bearing 18 faces the hub 10 in front.Towards the inside of the centrifugal rotor 2, the front sealing bearing18 with the hub 10 defines an inlet chamber 20 with an annular opening22 upstream of the inlet chamber 20. Towards the exterior, the frontsealing bearing 18 is machined to enable it to create a seal of thecentrifugal rotor 2 in rotation within the housing 4. For example, aseal may be used, such as for example a labyrinth ring 24, as aninterface between the centrifugal rotor 2 and the housing 4. As can beseen in the figures, the centrifugal rotor 2 also includes a furthersealing bearing 18 on the downstream side, or a rear sealing bearing,which extends from the downstream flange 14 and receives anotherlabyrinth ring 24.

The channels driving air between the upstream flange 12 and downstreamflange 14, each have an outlet 26 (FIG. 1) radially oriented at thelargest diameter of the flanges. The air then enters a diffuser 28 inwhich it is guided so that the air flow is more longitudinal thanradial. The channels 30 in the diffuser 28 also make it possible toconvert the helical movement of the air flow to a substantially straightmovement.

FIGS. 2 and 4 illustrate a first embodiment of a centrifugal rotoraccording to this invention. As shown in the drawing, the overallstructure is substantially the same in FIG. 1 and in FIGS. 2 to 4. Thus,the references in FIG. 1 are used in FIGS. 2 to 4 to designate similarelements. A centrifugal rotor is thus found 2 rotatably mounted in ahousing 4 around a shaft 6 having a longitudinal axis 8. The centrifugalrotor 2 is sealed off relative to the housing 4 thusly ensured inparticular through the sealing bearings 18 working together with thelabyrinth rings 24 (or other type of seal). A hub 10 enables aconnection between the rotor and the shaft 6, for example by means of aspline that is not shown. The centrifugal rotor 2 further comprises anupstream flange 12 and downstream flange 14 interconnected by vanes 16.The upstream flange 12 has a sealing bearing 18 which with the hub 10defines an inlet chamber 20 of the annular opening 22. Again, when thecentrifugal rotor 2 rotates around the longitudinal axis 8 of the air(or other fluid) is being drawn through the opening 22 (longitudinalsuction) to be compressed in a helico-centrifugal motion and then againbecome longitudinally oriented within a diffuser 28 optionally providedwith channels.

The differences between a rotor of the prior art and a centrifugal rotor2 according to this invention are essentially located at the outputs 26,that is to say at the area having the greatest diameter of the upstreamflange 12, of the downstream flange 14 and the vanes 16.

Compared with centrifugal rotors of a compressor (or pump) known in theprior art, this invention proposes to provide an outlet for air flow ina centrifugal rotor (or other fluid) having an improved velocity vectorto enter into the longitudinal diffuser. For this purpose, it isexpected that the air channels will be slightly bent (defined by theflanges and the vanes) in the centrifugal rotor 2 close to the outlets26. A curvature is thus produced at the output of the centrifugal rotorwhich makes it possible to increase the speed of the air towards theoutside of the curvature.

While in the embodiment of FIG. 1, it is noted that the inner face ofthe upstream flange 12 and the surface of the downstream flange 14 aresubstantially plane (and slightly converging), the inner surface of theupstream flange 12 has, near the output 26, a concave area 32 and theinner surface of the downstream flange 14 has, near the outlet 26,opposite the concave area 32, a convex area 34.

If we then consider a surface 36 tangent to the inner surface of thedownstream flange 14 at the outlet 26, this surface is substantiallyconical (cone axis of the longitudinal axis 8) and forms, with a radialplane illustrated by a dotted line, angle a. In the embodiment of FIG.2, this angle is about 15° and it is about 30° in the embodiment of FIG.3. Preferably, this angle will be comprised between 10° and 45°. In thecentrifugal rotors of the prior art, as illustrated by FIG. 1, thisangle is substantially zero.

To avoid overloading the Figures, the surface tangent to the innersurface of the upstream flange 12 was not illustrated. A substantiallyconical surface is also found here, around the longitudinal axis 8,which forms, with the radial plane illustrated, an angle which ispreferably less than 45°, for example between 10 and 45°.

FIG. 4 illustrates that the vanes 16 extend into the convex area 34 ofthe downstream flange 14. Of course, they extend in a similar mannerinto the concave zone 32 of the upstream flange 12. Preferably, asillustrated in this FIG. 4, the vanes 16 extend to the peripheral edgeof the upstream flange 12 and the downstream flange 14, that is to say,up to the output 26 of the rotor.

In FIG. 3, H is referenced by the line having the greatest diameter ofthe inner surface of the downstream flange 14 and by S for the linehaving the greatest diameter of the inner surface of the upstream flange12. S and H are circles the center of which lies on the longitudinalaxis 8. R_(S) and R_(H) radius respectively. As is apparent from FIG. 3(this is also visible in FIG. 2 but slightly less pronounced),R_(S)>R_(H). Thus, for a same average speed over the air outlet surfaceoutside the centrifugal rotor 2, the peripheral speed of the air in thevicinity of point S is greater than that of the air near the point H.This also applies to the absolute tangential velocity. The air isaccelerated from the upstream side (exterior to the exiting “turn” ofthe rotor), thereby making it possible to have a more uniform speed atthe input of a substantially longitudinal section of the diffuser.Therefore, the losses in pressure, if only within the diffuser, arereduced and therefore make it possible to increase the yield of thedevice.

The shape of the centrifugal rotor according to this invention thusallows a more gradual transition from a radial air flow to alongitudinal flow. The distribution of fluid velocities through apassage section of the diffuser is more uniform and regular. Thepressure drops are thus limited and again in terms of yield is obtainedat a time when the fluid passes from an essentially radial flow to anaxial flow as it flows into the axial diffuser.

Note that the channels in the centrifugal rotor 2 have a passage inwhich the flow is substantially radial. The inner surfaces of theupstream flange and the downstream flange each have an inversion ofcurvature. And the inner surface of the upstream flange 12 has a convexarea near the inlet chamber 20 and then it extends from the hub 10 aftera curved area, said inner surface has a concave area as described above.And the inner surface of the upstream flange 14 has a convex area nearthe inlet chamber 20 and then it extends from the hub 10 after a curvedarea, said inner surface has a concave area as described above. Thetrajectory of the fluid in the channels defined by the flanges and thevanes in the centrifugal rotor 2 and thus has a curve.

To better guide the fluid in the curved rotor, the vanes 16 extend intothe curved region (that is to say up to the concave area of the innersurface of the upstream flange and to the convex area of the innersurface of the downstream flange) and guide the fluid preferably to theoutlet 26. The blades 16 thus are also curved. They preferably extendfrom the inlet chamber 20 to the line H and the line S. or for exampleup to the vicinity of these lines (to least 10 mm in these lines).

Of course, this invention is not limited to the preferred embodimentsdescribed above as non-limiting examples, but it also relates to thevariants within the reach of those skilled in the art.

It also concerns variations on the embodiment that will be found withinthe scope of professionals in the field within the framework of theClaims below.

1-10. (canceled)
 11. A centrifugal rotor (2), comprising: a hub (10)having a longitudinal axis (8); a fluid inlet (20); a first flangeupstream (12) and having an opening (22) around the hub (10); a secondflange (14) separated downstream from said first flange by vanes (16)thereby forming channels each delimited by the first flange (12), thesecond flange (14) and two of the vanes (16) extending from the fluidinlet (20) to a peripheral outlet (26); wherein at a proximity of theperipheral outlet (26), the first flange (12) includes a concave area(32) oriented towards the channels, and the second flange (14) includesa convex area (34) oriented towards the channels.
 12. The centrifugalrotor of claim 11, wherein the first flange (12) and the second flange(14) comprise a circular shape around the longitudinal axis.
 13. Thecentrifugal rotor of claim 11, wherein a surface tangent to the concavearea of the first flange (12) exiting the channel forms an angle ofbetween 1° and 45°, with a radial plane perpendicular to thelongitudinal axis (8).
 14. The centrifugal rotor of claim 13, whereinthe surface tangent (36) to the concave area of the first flange exitingthe channel forms an angle of between 10′ and 30°, with a radial planeperpendicular to the longitudinal axis (8).
 15. The centrifugal rotor ofclaim 11, wherein the surface tangent (36) to the convex area (34) ofthe second flange (14) exiting the channel forms an angle of between 1°and 45°, with a radial plane perpendicular to the longitudinal axis (8).16. The centrifugal rotor of claim 15, wherein the surface tangent (36)to the convex area (34) of the second flange (14) exiting the channelforms an angle of between 10° and 30°, with a radial plane perpendicularto the longitudinal axis (8).
 17. The centrifugal rotor of claim 11,wherein the vanes (16) extend to at least one of a peripheral edge (H,S) exterior to the first flange (12) and the second flange (14).
 18. Thecentrifugal rotor of claim 11, wherein the first flange (12) includes anouter peripheral (S) edge adjacent to the channels which have a greaterdiameter (R_(S)) than another diameter (R_(H)) of an outer peripheraledge (H) adjacent to the channels of the second flange (14).
 19. Acentrifugal compressor, comprising a centrifugal rotor (2) of claim 11.20. A centrifugal pump, comprising a centrifugal rotor (2) of claim 11.